Design of the database

Database design process and data description

1. Requirements Analysis Phase (accurate understanding and analysis of user needs including data and processing)

2. Conceptual structure design phase (to form an independent DBMS conceptual model by synthesizing, generalizing and abstracting the user's needs)

3. Logical Structure design phase (transforms the conceptual structure into a data model supported by a DBMS and optimizes it)

4. Database Physical design phase (select a physical structure (including storage structure and access method) that best suits the application environment for the logical data model)

5. Database implementation phase (the designer uses data languages, tools and host languages provided by the DBMS, builds databases based on logical and physical design results, compiles and debugs applications, organizes data into storage, and debugs)

6. Database operation and maintenance phase (evaluation, adjustment and modification of database system during operation)

The design pattern of structural design in the process of database design

(1) The formation of independent machine features at the conceptual design stage, independent of the conceptual model of each DBMS product, discusses the E-r diagram

(2) in the logic design stage, the e-r is replaced with the data model supported by the database product, such as the relational model, form the database logical pattern, then establish the necessary view on the basis of the basic table, and form the external model of the database.

(3) in the physical design phase, according to the DBMS characteristics and processing requirements, physical storage arrangements, indexing, to form a database model

Characteristics of database Design

(1) database construction is a combination of hardware software, and development (technology management and interface)

(2) from the software design point of view, the database design should be combined with the application system design, that is to say, the whole design process to the structure (data) design and behavior (processing) design closely together.

What are the design objectives of the requirements analysis phase? What is the content of the survey?

Design Objective: To fully understand the work profile of the original system (manual system or computer systems) through a detailed survey of the real-world processing objects (organization, department, Door, Enterprise, etc.), identify the various needs of the users, and then determine the new system functions on the basis.

The content of the survey is data and processing, i.e. the following requirements for the database:

(1) Information needs, refers to the user needs to obtain information from the database content and nature, by the information requirements can be everywhere data requirements, that is, in the database need to store what data

(2) processing requirements, refers to the user to complete what processing functions, the processing of the corresponding time what requirements, processing methods are batch processing or online processing.

(3) Security and integrity requirements.

What is the content and function of the data dictionary

(1) data item, (2) data structure, (3) traffic, (4) data storage; (5) process

Where the data item is the smallest constituent unit of the data, several data items can form a data structure, and the data dictionary describes the logical content of the data stream and the data storage by defining the data items and structure.

The role of data dictionary: Data dictionary is about the database description, in the requirements analysis phase, is the next step in the conceptual design of the basis, and in the database design process constantly modified, enriched, perfect.

The conceptual structure of the database? The characteristic and design strategy of the trial statement

Conceptual structure and conceptual conceptual model, the main features are:

(1) can really reflect the real world, including the relationship between things and things, to meet the user's data processing requirements, is a real world model

(2) Easy to understand, so that you can use it and unfamiliar computer users to exchange views, the active participation of users is the key to design success (3) easy to change, when the application environment and application requirements change, easy to modify and expand the conceptual model

(4) Easy to switch to relational, network, level and other data models

Conceptual structure design strategies typically consist of 4

(1) Top-down, that is, the first definition of the global conceptual structure, and then gradually refine

(2) Bottom-up, that is, first define the conceptual structure of each local application, and then integrate them to obtain a global conceptual structure.

(3) Gradually expand, first define the important core conceptual structure, and then want to expand, a snowball way to gradually generate other conceptual structures, until the overall conceptual structure.

(4) hybrid strategy, combining bottom-up and top-down, to design a framework of global conceptual structure with top-down strategy

The importance and design steps of database conceptual structure design

Importance: The database conceptual design is the key to the whole database design, and the application requirements will be abstracted into the conceptual structure and then the other requirements as the basis in the requirement analysis stage.

Design steps: There are many design methods of conceptual structure design, the most frequently used method is bottom-up, the design step of this method has two steps: 1 is abstract data and design local partial view, the second part is integrated partial view, get global concept structure.

What is a e-r diagram? What are the basic elements of the E-r diagram?

(1) The E-r diagram is an entity-contact diagram that provides a conceptual model for representing the entity type, attributes, and contact methods used to describe the display world.

(2) The attribute, represented by an ellipse, is connected with the application entity with no edge.

(3) Contact, with a diamond, the diamond box is indicated by the contact name, and with the non-edge respectively connected with the relevant entities, at the same time in the non-edge of the type (1:1,1:n or m:n)

What is a database logical design?

(1) Transform the conceptual structure into a general relationship, a mesh, and a hierarchical model

(2) Transforming a transformed relationship, mesh, and hierarchy model into a data model supported by a specific DBMS

(3) Optimization of the data model

Rules for converting E-R diagrams to relational models

An entity type is converted to a relational model. The entity attribute is the relationship attribute, and the entity code is the relationship code.

Design of the database